1. Field of the Invention
The present invention relates to a control method for a light control apparatus and to a light control apparatus.
2. Description of the Related Art
With sophistication of portable devices having an image pickup function and small-size optical apparatuses such as micro videoscopes in recent years, there are demands for improvements of the optical components such as lenses and stops used therein. Specifically, there are increasing demands for replacement of conventional fixed focal length lenses and fixed aperture stop respectively with adjustable focus lenses and variable stops. Furthermore, stable operations of the optical components, not to mention to further size reduction and power saving, are desired.
FIG. 12A is a graph showing changes in the quantity of light with time in a conventional light control apparatus, and FIG. 12B is a graph showing changes in the drive current with time in the conventional light control apparatus. In a prior art light control apparatus described in Japanese Patent Application Laid-Open No. 2007-25357, a control method with which re-exposure due to bouncing of the shutter after it is fully closed is prevented from occurring while allowing high speed shutter operations. In this light control apparatus, furthermore, a high current is applied during the period from the time at which the shutter blades start to close to the time at which the shutter is fully closed, and a low current is applied after the shutter is fully closed, whereby the movement of the shutter is stabilized, and re-exposure due to bouncing is prevented.
However, in the light control apparatus described in Japanese Patent Application Laid-Open No. 2007-25357, the shutter is always driven by a constant drive current in the shutter operation. In consequence, if the drive current required to drive the shutter changes due to influences of the condition in the environment such as the temperature or humidity or due to a deterioration of a coil or magnet with time, the shutter cannot operate stably.